The human protein Caprin1 is a prototypic member of a novel protein family that plays many essential functions, including promoting cellular proliferation, mediating innate antiviral response, regulating neuron development, and participating in stress response. Caprin1 has been implicated in the pathogenesis of many human diseases such as cancer, viral infection, hearing loss, and neurodegenerative disorders. The various functions of Caprin1 are dictated by its interaction with various partners. It is therefore crucial to reveal the molecular structures of Caprin1 protein complexes. We have recently determined the crystal structure of the dimerization domain of human Caprin1, representing the first structural study of this important protein. Building on this success, a combined structural and biochemical study is proposed to further investigate the molecular basis for Caprin1 functions, with an emphasis on its interaction with partner proteins including G3BP1, FMRP, and the Japanese encephalitis virus core protein. Results from the study will provide the much needed structural knowledge regarding the function, regulation, and specificity of Caprin1.